1. Field of the Invention
The present invention relates to a tool stocker for holding and storing a plurality of tools that can detachably be mounted on a main spindle for machining a workpiece, a machine tool system that incorporates such a tool stocker therein, and a tool damage detecting apparatus for use in a machine tool system.
2. Description of the Related Art
Generally, machine tool systems have been used in the art, which have a tool stocker for holding and storing a plurality of detachable tools, and which machine a workpiece in various machining modes with tools selected from the tool stocker, wherein the tools are replaceably mounted on a main spindle. Such machine tool systems should preferably take up a small area in order to improve installation space efficiency and to facilitate the transfer of workpieces between adjacent machine tools. It is preferable for a machine tool system to have a small width as viewed in front elevation, in light of the relationship of the machine tool system to other apparatus within the factory. However, the machine tool system needs to have a sufficiently large tool stocker and a sufficiently large number of stored tools.
Japanese Laid-Open Patent Publication No. 2007-125642 discloses a tool exchange apparatus combined with a machine tool, which has a main tool stocker for storing tools and an auxiliary tool stocker for storing fewer tools than the main tool stocker, so that the tool exchange apparatus can hold an increased number of tools without increasing the installation space. A tool in the main tool stocker is transferred to a main spindle as follows: A tool pod which stores the tool is turned 90° and then the tool is pulled out of the tool pod by a turn arm. The tool is then turned 180° by the turn arm and is inserted into (mounted on) the main spindle. A tool in the auxiliary took stocker is similarly transferred to the main spindle.
In systems that use a number of tools, it is important to grasp the states of the respective tools in order to carry out smooth and automatic machining operations, and also in view of cycle times. For example, in the event that a tool becomes damaged by seizure or the like during a machining process, it is desirable to quickly detect damage to the tool and to replace the tool if necessary in order to avoid a system shutdown.
Japanese Patent No. 3369712 discloses a tool damage detecting apparatus incorporated within a turret system for machining a workpiece mounted on a slide unit, which has been moved into a machining position. The slide unit supports thereon a machining head (gang head) on which a plurality of main spindles are rotatably mounted. The turret system includes four machining units disposed around a turn shaft, each having a plurality of tools, wherein the machining units are turned and indexed around the axis of the turn shaft. One of the machining units, which is indexed to a low position, is used to machine a workpiece, whereas the tool damage detecting apparatus is disposed in association with the machining unit, which is indexed to an upper position opposite to the low position.
The tool exchange apparatus disclosed in Japanese Laid-Open Patent Publication No. 2007-125642 is required to perform at least three different actions when transferring a tool from the main tool stocker or the auxiliary tool stocker to the main spindle, including pulling a tool from a tool pod, turning the tool with the turn arm, and inserting the tool into the main spindle.
The above operations for transferring the tool are complex, and involve turning of the tool. Therefore, such operations tend to cause a tool transfer failure, due to positional misalignments between the tool stockers and a tool gripper of the main spindle, as well as dislodgment of the tool from the turn arm.
Since the tool is turned by the turn arm, it is likely to cause the machine tool to wobble laterally and vibrate, possibly lowering the accuracy with which workpieces can be machined, and producing noise. Such lateral wobbling movement and vibration should desirably be held to a minimum, particularly in space-saving systems having a reduced width as viewed in front elevation.
The tool damage detecting apparatus disclosed in Japanese Patent No. 3369712 serves to detect damage to a plurality of tools on a certain machining unit of the turret system.
If the machining units are assigned successive letters “a” through “d” from the machining unit in the lowest position for machining the workpiece, then the machining unit in an upper position associated with the tool damage detecting apparatus is identified by “c”. If the turret system is controlled to machine the workpiece with the machining unit “a” initially in the lowest position, then to machine the workpiece with an adjacent machining unit “b” brought into the lowest position, and thereafter to machine the workpiece again with the machining unit “a” brought into the lowest position, in this case, the machining unit “a” is unable to reach the tool damage detecting apparatus over a plurality of machining cycles. Consequently, even if a tool used by the machining unit “a” becomes damaged during the first machining cycle, the damage will not be detected by the tool damage detecting apparatus and the tool will continue to be used. Stated otherwise, if the workpiece is machined continuously only by a certain machining unit, without the turn shaft being rotated, then damage to a tool in the machining unit will not be detected.
One solution would be to rotate the turn shaft to enable the tool damage detecting apparatus to detect tool damage each time that a machining unit machines the workpiece. However, in this case, system downtime is increased and the cycle time is extended.